This invention relates generally to the field of ophthalmic surgery and more particularly to ultrasonic hand pieces for phacoemulsification.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting needle is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting needle liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven hand piece, an attached cutting needle, an irrigating sleeve, and an electronic control console. The hand piece assembly is attached to the control console by an electric cable and flexible tubing. Through the electric cable, the console varies the power level transmitted by the hand piece to the attached cutting needle and the flexible tubing supply irrigation fluid to and draw aspiration fluid from the eye through the hand piece assembly.
The operative part of the hand piece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting needle during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the hand piece by flexible mountings. The hand piece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting needle. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting needle is adjusted so that the needle projects only a predetermined amount past the open end of the irrigating sleeve.
In use, the ends of the cutting needle and irrigating sleeve are inserted into a small incision of predetermined width in the cornea or sclera. The cutting needle is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting needle communicates with the bore in the horn that in turn communicates with the aspiration line from the hand piece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting needle, the cutting needle and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline solution or irrigating solution that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting needle.
During surgery, the console controls irrigation and/or aspiration which in turn determines the pressure in the eye. Aspirating too much fluid from the eye can result in low pressure and a shallowing or collapse of the anterior chamber. Typically, the pressure in the eye is monitored by measuring the pressure in the irrigation and/or aspiration lines. One or more noninvasive pressure sensors are located in a fluidics cassette to which the irrigation and/or aspiration lines are connected. The location of these pressure sensors, in a cassette that is remotely located from the eye, leads to some delay in monitoring pressure in the eye. It would be desirable to locate a pressure sensor close to the eye to minimize the delay in monitoring eye pressure.